The present invention relates to apparatus and/or process for controlling an air fuel ratio for an internal combustion engine in accordance with an oxygen content sensed by an exhaust gas sensor disposed in an exhaust passage of an internal combustion engine, and to apparatus and/or process for detecting activation of an exhaust gas sensor.
A published Japanese patent application No. S58(1983)-193454 (≈DE 33 05 699 A1) shows an oxygen sensor which can be used as an exhaust gas sensor for an air fuel ratio control system for an internal combustion engine. This sensor is of a quasi reference electrode type which does not use the atmospheric air at a standard electrode. An oxygen sensor of this type includes a solid electrolyte film sandwiched between anode and cathode and an electric circuit for applying a bias voltage between the anode and cathode. The oxygen content is sensed by measuring a potential difference between both electrodes in the state in which the bias voltage is applied and an oxygen partial pressure is controlled between both electrodes.